Method of removing gas from the cavity and stabilizing the core during injection molding

Abstract

The method and apparatus includes an injection molding assembly including a mold, a core and a mold cavity therebetween wherein said mold cavity has a base, a peripheral area of said base and a central area of said base, at least two injection gates for injecting plastic material into said mold cavity situated adjacent the peripheral area of the mold cavity in a substantially balanced fashion, a source for injecting plastic material through the injection gates whereby molten plastic advances from the injection gates in the mold cavity to force gas in advance of the plastic and to stabilize the core, and means for venting the gas from the mold cavity.

What is claimed is: 
     
       1. A method which comprises: providing an injection molding assembly including a mold, a core and a mold cavity therebetween, wherein said mold cavity has a base, a peripheral area of said base and a central area of said base; injecting molten plastic material into said mold cavity through at least two injection gates, wherein said injection gates are situated adjacent the peripheral area of said mold cavity in a substantially balanced fashion generally equidistantly spaced from each other with a substantially symmetrical disposition, whereby molten plastic advances from the injection gates in the mold cavity to force gas in advance of the plastic and to stabilize the core; including in addition injecting molten plastic material through an injection gate positioned adjacent the central area of said base, wherein molten plastic is first injected through the central gate followed by injecting molten plastic through the peripheral gates and including the step of maintaining the peripheral gates at a lower temperature than the central gate; and venting the gas from the mold cavity. 
     
     
       2. A method according to claim 11 including in addition injecting molten plastic through four injection gates positioned circumferentially adjacent the peripheral area of the base. 
     
     
       3. A method according to claim 1 including in addition injecting molten plastic through two injection gates positioned adjacent the central area of said base.